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The Life Cycle of the Variola Virus

Variola virus is an infectious virus that causes the disease smallpox. Smallpox is an extremely contagious and often fatal disease. Outbreaks of the disease have occurred for thousands of years. Because of international efforts to implement a worldwide vaccination program within the latter half of the 20th century, smallpox has been eradicated.

  1. Forms of the Disease

    • Variola major and variola minor, the most common forms of the disease, present with similar signs and symptoms. Variola major is fatal in 30 percent of the infected population, while variola minor is fatal in less than 1 percent. Two rare forms of smallpox called hemorrhagic and malignant smallpox are inevitably fatal.

    Incubation Phase

    • Smallpox is spread from one person to another by direct and long-term contact. Items such as clothing that come in contact with the infected person and body fluids can also spread the disease. Smallpox is rarely transmitted through the air and is not transmitted by animals or insects.

      The incubation period lasts anywhere from seven to 17 days, during which infected individuals are often asymptomatic. Infected individuals are not contagious during this time.

    Initial Phase

    • Persons with smallpox initially have symptoms of high fever between 101 and 104 F, head and body aches, malaise and occasional vomiting. This phase lasts about two to four days during which time the infected individual may be contagious.

    Early Rash Phase

    • This is the most contagious phase of the illness, lasting approximately four days. Tiny red dots will appear on the tongue and the inside of the mouth and progress to open sores. Soon after, a rash will appear on the skin. It will first affect the face, then the torso and extremities.

      Around the third day, raised bumps will appear in the rash. On the fourth day, thick, cloudy fluid will fill the bumps. These will often have a bellybutton-like depression in the center. At this time fever may recur and remain until the bumps scab over.

    Pustular Rash and Scabs Phases

    • Bumps within the rash will eventually become raised sores that are firm to the touch and round. The pustular rash usually lasts for about five days. After about five more days, the sores will begin to ooze, forming a crust and subsequent scabs. During these phases, the infected individual is contagious.

    Resolving Scabs

    • Inevitably, the scabs will fall off and scars will form. It usually takes about six days for the scabs to completely resolve. During this time the individual is still contagious. After this time, all the scabs will fall off and the person will no longer be contagious.

    Treatment

    • Vaccines are available to provide immunity against smallpox. These can be administered up to four days after exposure to provide immunity. However, at this time, there is no known treatment for an active infection of smallpox other than to manage the symptoms. Because of the extreme virulence of smallpox, outbreak management must be implemented immediately to prevent an epidemic.

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